Planar, microstrip antennas have characteristics often sought for portable communication devices, including advantages in cost, efficiency, size, and weight. However, such antennas generally have a narrow bandwidth which limits applications. Several approaches have been proposed in the art in an effort to widen the bandwidth of such structures. One such approach is described in U.S. Pat. No. 5,572,222 issued to Mailandt et al. on Nov. 5, 1996, for a Microstrip Patch Antenna Array. Here, a microstrip patch antenna is constructed using an array of spaced-apart patch radiators which are fed by an electromagnetically coupled microstrip line. Generally, with such structures, electromagnetic coupling between radiators is negligible, as it is regarded as a second-order undesired effect. Mailandt's structure is contemplated for use in fixed communication devices. For portable communication devices, size and weight considerations are paramount and such structures may not be suitable. Many other prior art approaches have similar drawbacks.
Communication signals are usually filtered using a band-pass filter or the like to remove unwanted harmonics before being sent to an antenna for transmission. Such filtering adds to the cost and complexity of a product. Planar patch antennas have been proposed that provide some band pass filtering. For example, it is known to selectively shape a radiator patch to provide narrow-band limited filtering. It is desirable to provide band pass behavior, with strong rejection of undesired side-band noise, in a cost effective manner. Planar patch antennas could provide a part of the solution if bandwidth concerns are addressed, and more effective band-pass filtering provided. Therefore, a new approach for a pass-band planar antenna is needed.